The long-term goal of this project is to explain the logic by which chemical signals are encoded, and to elucidate basic principles of the organization and development of the neurons that encode them. The experimental plan takes advantage of the fruit fly Drosophila melanogaster as a model system, which allows incisive molecular genetic analysis of chemosensory genes as well as physiological and behavioral analysis of chemosensory function. The project investigates a new family of 30 predicted chemoreceptor genes, the IR20a family, whose expression and function are completely unexplored. The first aim is to map these genes to neurons of chemosensory organs in the adult fly, and to examine their projections in the central nervous system. The aim is designed to address a major problem in sensory biology: how a sensory system integrates the multiple inputs that are ultimately translated into a behavioral response. A likely outcome of this aim is that it will support the identity of the IR20a family as a major new family of invertebrate taste receptors. The second aim is to produce a receptor-to-neuron map in the larval stage. The coexpression of these receptors with each other and with other classes of chemoreceptors will be analyzed. Their developmental profile and cellular location of expression in neurons will be determined. This aim is expected to support the identity of these receptors as a major new family of larval taste receptors. The third aim tests the function of these receptors directly. Hypotheses concerning roles in chemoreception and in neuronal development will be tested through physiological and behavioral measurements, and by examination of neuronal morphology and projections. A model in which they play a dual role in the regulation of feeding will be tested. The molecular and cellular basis of feeding regulation has major implications for public health. Diseases carried by insects afflict hundreds of millions of people each year, and many of these insects locate their human hosts and their mates through chemosensory cues. Advances in the understanding of chemosensory reception may lead to new means of controlling these insect vectors of human disease.